Not sure what Claydon did at MGS, but Moody(head from 1966-71) phoned parents as soon as he’d caned you. Bastard!
Detentions were initially Saturday mornings only, so no problems swaggering into school, telling your parents you’d got rugby practice or the like. Moody changed it to after school, so you now just told them you were helping out in the Cinema Club or something!!
No record went to parents, but there was a buff file for every pupil & details of it all was in there. and don’t ask how I know it’s a long story.
From what I remember, public schools & part-boarder schools(like Manchester Grammar) were the sort who kept a running record that went onto the end-of-term report book. Not many grammars did in my time(63-70), though there were a few, I believe.